Concentration of brines



May 14, 1929. w. E. BURKE er A.

CONCENTRATION OF"BRINES Filed Feb. 6, Y1924 8 Sheets-Sheet l INVENTOR5 'ATTORNEYS May 14, 1929 w. E. BURKE ET AL 1,712,787 l CONCENTRATION OF BRIN Filed Feb. 6, 1924 8 Sheets-Sheet 2 l /Vaz C05 A3612) l ATTORNEY;

May 14, 1929.

W. E. BURKE ET AL CONCENTRATION OF BRINES 8 Sheets-Sheet 3 Filed Feb. e, 1924 MK mi m,

May 14, 1929.

Mms PER m00 M025 @fh/,47m

Mozs Pff? mao om @fu/Affi A40/ 5 PER /000 M015 fl/14475,?

w. E. BURKE Erm. 1,712,787 CONCENTRATION OF BRINES Filed Feb. 6, 1924 8 Sheets-Sheet 4 ATTORNEYS ff I May 14 1929- w. E. BURKE 'ETA-L 1,712,787

CONCENTRTIO 0F BRINBS Filed Feb. e, 1924 a sheets-sheet 5 M015 Pfff moa/vols afnam? 'PMA-,MMM

` ATroRNEYs May 14, 1929 w, E. BURKE ET m. 1,712,787

l'c'n'uNclaNTNATIoN oF' BRINEs Filed Feb. 6, 1924 s sheets-Sheet 6 Naz CL2 Mms PEI? moo/vow @fn/ATER o J1 0 60 1 O 0C Tem/oem ture Naf.;

Mms Pff? /000 ,vom of W4 Tfn Q 2o 4o 6o ao 1 0 "C Tempera h/re l M1" s' INVENTORS {fi/ulb( l Il# ATTORNEY;

May 14, 1929.

M015 PER Ml afl/1447671 W. E. BURKE ET AL GONCENTRATIQN vor" Bnrmss File-a Feb. 6,1924 l 8 Sheets-Sheet 7 I 771 j 2.9 fz 7 EN 'n 20 eo 100 0C 60 Te mp vgraff/re ATTORNEYS May 14, 1929.

w. E. BURKE ET AL 1,712,787

CONCENTRATION OF BRIN's Filed Feb. e, 1924 @Lgf/7 8 Sheets-Sheet 8 Concenrafr'an. of /fg C73 /h r/'ne 7b PrevenZ Preczpz'fa/on of /Vczhg C/,g

ATTORNEYS v Patented May 14, 1929.y

AI JNirEn STATES 12..1121191'1'l OFFICE-.j

WILLIAM r. BURKE Alm HARALD enormer rnoNA, cALnz-onmm AssIeNons, BY

MESNE ASSIGNMENTS, TO AMERICAN 'NEW YORK, N. Y., A CORPORATION OF DELAWARE. y

POTASH CHEMICAL CORPORATION, OIF

coNcmaA'rIoN or nantis.

Application medebruary' e, 1924. ,seiai no. 690,946.

lThis invention relates to the treatmentof brines such as are found in Searles Lake, California, and brines'of similar composition, for the concentration of' potassium chloride s therein andthe recovery ofpotassiumchlof ride in a high state of purityfrom'the conf centrated brines. Searles Lake brine is of complex composition, and consists mainlV of the chlorides,

11o sulphates, carbonates, an borates of sodium and potassium. l It has heretofore been "proposed to treat such brine for the recovery of potassium chloride, but in general, the yieldsv of pure potassium chloride have been -low, ia 'or where high yields have been obtained the. potassium" chloride has been impure. It is a primary object of the, present inventionto Vproduce potassium chloride and borax Afrom Searles Lake brine, and brine ofsimilar coln- 1 2o osition, and obtain potassium chloride of a high' degree of purity and with increased yield. The present invention enables an economical and high recovery of the potash contentyof thef-brines inthe form of potassium chloride'f ahigh degree of purity, While also i enabling borax-to be similarly recovered.

Inordert avoid loss of -potash during the concentration of the brine, it is necessary to prevent precipitation and loss'of the potash.l

3o in the'form of insoluble salts during concen-v potassium chloride, it is important that the concentration of the brine be' carried to a high degree such as will permit the separa- .tion of substantial 'amounts of potassium chloride in a pure state ol`1 cooling. It is also important that the concentrated brine be of suitable composition, and the cooling car ried out in such manner, that little or no salts other than potassium chloride will separate with the potassium chloride during the crystallization thereof on cooling.' These desirable results have not heretofore beenobtained during recovery of potassium 'chloride from brines of the character described; but they can readily be obtained by the process of the" present invention and an economical and very high recovery of the potash content of the brmes can thus be secured. A further marked ladvantagle of the process of the present invention askin the fact that suit tration. In order to obtain ahigh yield oil4 le control conditions -with consequent uniformity of 'product may be readily and uniformly maintained under conditions of comercial operation. y

One of the difficulties presented 'in the treatment of brines. such as Searles Lake j brine, containing the sulphates and chlorides of both sodium and potassium, is due to the tendency to form a double sulphate of sodium and potassium having the composition NaSO,.3K,SO-`4 or K Na (S04) 2. When such a brine is evaporated at temperatures above 11.4 C. this double sulphate, glaserite, which ishmuch less soluble than potassium chloride, tends vto saturate the brine so that the brine becomes saturated with respect to glaserite during concentration before it becomes saty urated with respect to potassium chloride, with the result that concentration of the brine 70 will cause precipitation of glaserite before the solution becomes saturated with potassium chloride. 'The precipitation of glaserite results in loss of potash in' that form, from which it has not been readily recoverable. In order to avoid precipitation of glaserite during concentration at moderate 'temperatures, the concentration must ordinarily 4be stopped'at a point short of that at which glaserite begins to form. If the concentration is stopped before glaserite begins to form, the brine will not be saturated with potassium chloride and only a low yield of potassium chloride can be obtained on cooling, 'while glaserite and sodium chloridema-y also separate in appreciable amounts along with the potassium chloride. If an attempt is made to obtain a higher concentration of potassium chloride or to saturate the brine with this salt, such further concentration is accompanied by a serious loss of potash as glaserite. The above conditions hold true at all temperature from 4.49 C. up to and above 1`00 C. when the brine contains no carbonate. When the brine contains carbonates, howa5 ever, we have found that under certain conditions, hereinafter pointed out, a double salt may be made to form, Ycontaining the carbonate and the sulphate of sodium, and having approximately the following composition: NazCO. 2Na2SO4. It contains about 26.9% of sodium carbonate and 73.1% sodium sul# phate, although in practieewe have found the composition to vary slightl and to be' somewhat higher in" sodium sulphate and somewhat lower in sodium carbonate than is indiv cated by the formula. It is less soluble in hot than in cold solutions and on concentration of the brine separates without water of crystallization. We have named this double salt Burkeite and we will use this name for convenience in referring tothis double salt in the present specification.

We have found that a potash brine of the Y class described, containing sulphates and carbonates, can be evaporated, under, suitably chosen and properly regulated evaporating conditions, to high concentrations at lower *temperatures and to saturation at higher temperatures with respect to potassium chloride without the formation of laserite. We have found that the presence o carbonates may be utilized to cause formation and precipitation of Burkeite, with consequent decrease in the y sulphate content of the brine, while preventing all formation of glaserite and while evaporating the brine to a high concentration or saturation with respect to potassium chloride. We have found that in a brine such as Searles Lake brine, the tendency towards formation of glaserite increases with decrease of temperature and ythat thetendency towards -formation of Burkeite increases with increase g higher temperature. This higher temperature must be not lower than a certain minimum value which is determined by the 'composition of the brine, and the advantages and economy of our process are increased as the final temperature of evaporation is increased to 100 C. or higher. We have also found that at lower temperatures such a brine may b e partially concentrated without formation lof glaserite and loss of potash values, but

that as the concentration progresses it is necessary to progressively increase the temperavture of the brine in order to prevent such glaserite formation.

B carrying out the evaporation at progressive y increasing and suitably chosen temperatures and completing the evaporation at a high final temperature, it is possible we have found, to make economical use of multiple effect evaporation and to thereby obtain a high final concentration with respectto potassium v chloride at the high final temperature while at the same time preventing glaserite from precipitating at any int during the concentration. Although gli; evaporation may be completed at temperatures somewhat below 100o C. we have found it advantageous to finish `the evaporation at temperatures of 100 C. or higher, for the reason that at these higher temperatures there is practically no possibility of laserite formation and the concentration o the brineswith respect to po- 'tassium chloride may be carried to a high degree, whereby a large and increased yield of potassium chloride may be obtained on the cooling of the concentrated brine. A further marked practical advantage of em loy'- ing such high final temperatures, we ave found, lies in the fact that whereas at lower temperatures the de of concentration must be regulated wit in very narrow limits in order to obtain, without loss of the tash values,'a concentrated brine from whic pure potassium chloride can be obtained on cooling, at the above higher temperatures the permissible limits Yof concentration to avoid loss and contamination are considerably extended. The reason for this lies in the fact that, as will be further indicated, loss of potassium chloride occurs if concentration is carried beyond the point of saturationwith respect to this salt, but that if the concentration with respect to potassium chloride is not carried beyond a certain minimum value at any 'ven temperature, there' will be an appreciable precipitation of sodium chloride 'together with the'pota-ssium chloride when the brine is cooled. At the higher temperatures there is an appreciable difference between these maximum and minimum values but at the lower .temperatures they approach each other so closely as to make a suitable control of the evaporation a very diicult matter. Our process therefore avoids loss of potash during concentration, while nevertheless attaining a high degree of concentration and also avoids contamination of the y,potassium chloride on crystallization, whilegiving a high' yield;

The present invention accordingly includes regulation an'd control of the concentration of the brine and of the temperature and composition of the brine during concentration with suitable removal of precipitated salts, so that sulphates will be removed as Burkeite along with sodium carbonate andthe excess sodium chloride during concentration, and so that a concentrated brine can be obtained of proper concentration and composition to permit a high recovery of potassium chloride of high purity therefromvby cooling. It also includes rapid cooling of such concentrated brine in conjunction with such regulation and control so that the potassium chloride may v be separated and' recovered practically free The process of the present invention is ad vantageously carried out in multipleA effect evaporators, e. g. in triple effect evaporators,

the raw brine, or the raw brine admixed with l mother liquor, being pumped into the last or low temperature efiect and from there being pumped through the remaining two effects in a direction countercurrent to that of the flow of steam through the system so that the final concentrationy is carried out at a high temperature.

If Searles Lake brine of usual composition is subjected to evaporation at a temperature of about 50 C., the brine will become saturated with glaserite before it is saturated with potassium chloride, and if the brine is further evaporated to increase the concentration with respect topotassium chloride, loss of potash as glaserite will take place; while if the evaporation is stopped efore .the brine becomes saturated with glaserite, the yield of potassium chloride obtained on cooling will be low, and the postassium chloride will be im ure.

e have found, however, that if the brine is evaporated at progressively increasing temperatures, as in a triple effect evaporator,

and if the temperatures and compositions in the differentl evaporator pans are properly regulated, the brine can be concentrated to saturation or a proximate saturation with,

potassium 'chloride without loss ofi' potash as glaserite during concentration. If a triple eect evaporator is used, the three evaporating pans may advantageously be maintained at temperatures of about 57 C., 80 C., and l10 C., a proportionate part of the water being removed in each successive evaporating pan and a proportionate part of the salts other than potassium chloride and borax being removed in each pan.

In order that the condition necessary for the Vformation of Burkeite and the removal of' sulphates thereby during concentration of Searles Lake brine and other brines may be maintained, and the evaporation carried out to substantial com letion in the manner indicated, 'we have etermined, as a result of extended investiga-tion, the solubility and equilibrium data required for controlling the evaporation. The results of our extended investigation are illustrated in a-somewhat diagrammatic and conventional form in the accompanying drawings, in which Figs, l to 5, inclusive, are equilibrium diagrams or plane projections of space models which graphically illustrate the composition of all possible aqueous solutions of the sulphates, chlorides and carbonates Aof sodium and potassium, saturated with sodium chloride at the respective temperatures indicated, and which also illustrate the nature of the solid salts which will be precipitated by isothermal evaporation and concentration of any such possible solutions, and in which Figs. 6 to 16, inclusive, are temperature-concentration diagrams or polytherms which graphically illustrate theequilibrium conditions at'the univariant points, such as H, I, Eq. 1 etc., in diagrams suchas Figs. 1 to 5, inclusive, for any temperature between 20 C. and 110 C., and from which other diagrams for any. temperature between these limits may be constructed. Fig. 2^ is a diagramlnatic and conventional representation of Fig. 2 in another aspect. In these drawings, the points in the space diagrams are designated by the same reference lcharacters as the polytherms from-which they may be determined. The significanceA and use 'of these equilibrium diagrams and polytherms will be readily understood by anyone skilled in the art.

The conditions existing in a solution which contains several dissolved salts are such that these salts are not necessarily present in their original form. Accurately, the composition of a'brine of the type with which we are concerned probably should be expressed in mols of Na, K, S04, Cl and CO3, but for convenience, the composition of the solution in equilibrium with any specified solid salts may be expressed in terms of combined mols of K Cl NaZCOS, etc. which has been done in this case. Moreover, because of the relations KCo3 Nagel, :Kzolg Nacio3 KES()4 l- Na2Cl2= I QCI2 -I- N @S04 the composition of any solution in such systems may be correctly expressed in terms of four, or less, such combinations.

This method of expressing the composition of the various possible solutions has been adopted in the polytherms, where the compositions of the solutions in equilibrium with various solid salts are stated in terms of K2Cl2, NazClz, NaZCO3 and Na2SO4. The curves on each polytherm figure represent the varying composition, with change of temperature', of a solution in equilibrium with the solid salts present at some one univa-riant equilibrium point. grams represent the limiting compositions of. all possible aqueous solutions saturated with sodium chloride .in the system Na, K, S04, Cl, CO3, at some one temperature. They are projections of space models formed by plotting the univariant points for thedesired ten'lperature, as shown in the plane of the diagram, erecting at each point a perand pendicular of which the length is proportion- TheA ,equilibrium diaal to the total number of mols of NaCOs, KZCOa, and NaZSO4 presentin the solution at that point,.an`d properly joining the ends of these perpendiculars. Neither the mols of NazCl2 nor of K2Cl2 are taken into account in determining the lengths ofthese perpendiculars, the former because they are not represented in the diagram and the latter in consequence of the relation To locate the-point Eq. 2 in Fig. 2 representing conditions at 57o C. for instance, we find from the polytherms of Fig. 15 that at this temperature this point represents a solution containing approximately 28 mols K2Cl2`, 3.5 mols Na2SO4, 31 mols Na()3 and 27 mols Na2Cl2 per 1,000 mols of water. The composition of this solution may equally Well be expressed as follows: 28 mols K2CO3, 3.5 mols Na2SO4, 3 mols NaZCOS, and 55 mols Na2C12. To locate this point we therefore measure `28 units to the left along the K2CO3 axis, then 3 units from this pointin a direction parallel to the Na. ,CO3 axis, and then .3.5 units to the right from the latter point in a direction parallelends of these perpendiculars.

at the point H since the soluto the NaZSO4 axis'. This locates the point Eq. 2 on the plane surface of the diagram. To locate the point in the space model erect a perpendicular at this point-having a length proportional to 28+3.5+3=34.5 units. The other .points are located in a similar manner. The space model is therefore formed by' locating the various points Eq. 2, Eq. 3 U, R, etc., erecting the corresponding perpendiculars at these points, 'and' properly connecting the No perpendicular is erecte ioi 1at this point contains only NazGl2 and Sodium chloride is not represented on the diagrams, because all the solutions represented are saturated Iwith respect to this salt. Sodium tetraborate and sodium metaborate are' not illustrated in the diagram because it has beenfound that the presence of these salts in an amount equivalent to 26 mols of B203 per 1000 mols of water, in the solutions represented by the diagrams, depresses the solubility of the sodium chloride somewhat, but produces no other marked change in the composition of the solution. Moreover, these diagrams represent equilibrium conditions which can be approaclied'but not always attained in actual practice. Accordingly, although these diagrams are not strictly accurate in the presence of the borates, or under plant conditions, they are suliciently accurate for practical purposes and indicate within fairly. narrow limits the changes which will take place int-he composition of a brine, and the'salts whichv may be separated or redissolved, under any given set of conditions. v

These or similar diagrams, therefore, in

*change in composition, due to conjunction with the dataA ofthe polytherms on which they are based, can be used in carryare constructed in the manner which has been described, and are bounded by the facesenclosed between the lines connecting thevarious points. Because of the relation between the .diierent salts, the composition of any aqueous solution of the sulphates, chloride and'carbonates of sodium and potassium, saturated with sodium chloride at. the indicated temperature, may be represented by a point in the space Within the s race model. The limiting compositions at/W ich the solution becomes saturated withff/'respect to one or more salts and at'which crystallization begins, are illu'strated by thevarious 'faces bounding the space model and by-the'lincs and points of intersectionof these faces. Each limitin face represents all possible compositions b solution saturated with respect to the salt indicatedand with respect to sodium chloride. Upon concentration at the indicated temperatures, the point representing the composition orf the solution cannot assoutside of the space enclosed by these aces, but at saturation with any particular salt moves along the face corresponding to that salt which is being precipitated out.

Prior to saturation of the brine with respect to any salt other than sodium chloride, the point representing the composition of the solution will lie within the space bounded by the faces of the diagram; and, upon concentration, that is, water removal, the point will move in a straight line, away from the origin and only sodium chloride will be precipitated until it strikes one of the bounding faces. This will be apparent from the fact that the relative proportions of the'other dissolved salts do not change, so .long as water only is removed, until the Y point representing the composition reaches a boundary and preci tation of the salt then reaching saturation gins; after which the point will move upon this boundary face in a line governed by the recipitation, until it strikes an edgeof the ace. It may then move upon this edge with simultaneous precipitation of the salts, or under certain conditions it may cross the boundary ed e with precipitation o f Aonlysodium chloride lhe composition o f the solution does not vary formly between the various equilibrium points and on vthe various crystallizationl areas In order to representexactly the compositions of all possible solutions these boundllt) ,evaporation ary lines andcrytallization arcas should be slightly curved, but for all practical purposes,

Athe diagrams as shown are 'suciently accurate tor use inthe carrying out 4of the proc.v

ess oi theineention.,

ltshould be especially noted `that the' Aequilibrium conditions shown in these diagrams hold'true only in brinesl saturated with respect to sodium chloride. Unsaturation with resp ,to this salt Awill 'alter the equilibrium relations out all the'salts, sometimes to a Very marlied extent.. ln the' practice of the invention it is necessary to maintain the briney saturated or nearly satura with respect to .sodium chloride duri concentration.

ldrinestrhich are dehcientin chlorides but' which contain the carbonatos and sulphates ot sodium and potassium can-be concentrated by the process ot the intention tor ecient recot'ery-o't potassium chloride atteraddition ot the necessary amount ot sodium clitoride., ln 'the absence ot sulhcient corides to maintain 'the conditions shonvn in the equilibrium diagrams, and embodied' in the process ot the'inintuitionLJ serious loss ot potash as glaserite may occur.1 p

ilhe application ot the equilibrium datato the process ot' the present intention will be illustrated by .specihc graphic illustrations ol the changes which talee place in the composition ot the brine during concentration by lille 1will use the equilibrium diagrams ol lEigs. 2., 3, and 4lshorring the solubilities at 57, 80 and lill" C.. tor this purposeD rlhe origin tl represents a brine saturated with sodium chloride but containing no other dissolved salt, Point di ot liig. 2

represents the original composition ot a brine such as @caries Lahe brine containing sulphates9 chlorides and carbonatos ot sodium potassium in solution but saturated with respect to sodium chloride onlyu lllntil this lili brine becomes saturated With respectto some other lsalt during evaporation, the increasing concentrations oit the other dissolved salts willbe in proportion to their original concentrations. 'lhe point representing the composition ol this solution at an moment during eraporation `ufill there 'ore more 1 along the prolongation oit the-line Ult until the point g is reached, at which point the solution is saturated with respect to sodium chloride and the salt represented by this tace in this case Burkeite,

During concentration by isothermal evaporation a solution in depositing its content gradually 1varies its composition array trom that ot a solution which is saturated with the substance being deposited and which .conf

tains nothing but this substance. Such a solution in this case is represented by point a, the'v crystallization Bur-keito. With furtherconcentration, therefore, the composition of this solution will be represented by points along the line g-B lying in the Burkeite face and drawn from the pointy through and away from the crystallization starting point for. Burheite. As the point representing the composition of the solution moves along this line,`"sodium chloride and Burkeite. will be precipitated by crystallization. The crystallization paths of any other solutions saturated with respect to sodiuml chloride and Burkeite would likewise lie in the lBui-keito face. alon lines drawn through and away lfrom the point a.

With continued evaporation at 57 C? the point representing the composition ol the original solution A would more along-` the line g-B'- until it reached the edge ot- Starting point for titl1 solutions haring compositions represented by pointsl lying along line bil-ltd. d until the point ldd. 2 is reached., rrhich'is the crystallization end pointn When this point is reached, no change in the compositionot. the solution will be caused by'turther erapo ltlll ration but simultaneous precipitation ol hurlreite, potassium chloride, sodium chloride and sodium carbonate monohydrate rrill taire place.

lit will be noted that under these conditions itis impossible to obtain a brine saturated with respect to potassium chloride without lirst *causing ilormation and precipitation oil the glaserite, with consequent loss ot potash. lt the brine should contain a higher concentration ot sodium carbonate relatiue to the concentrations oil the other constituents than is indicated tor the point its, this point will be rooted 4in a direction parallel to the sodium carbonate anisa Burlreite tace it Burlreite saturation is reached, to somehigher positionon the diagram representing the increased sodium carbonate concentration. -yWith a suciently high concentration ot" carbonate, it can be seen that the crystalliaation path dra-Wn trom a through the new saturation point corresponding to point g will strilre the edge oil the sodium carbonate ilace instead oit strihing the edge ot the glaserite tace. Evaporation oil such a brine would cause precipitation ot only sodium chloride, Burlreite and sodium carbonate monohydratc .until the brine be lltl or along the slope ot the' i ldd ' occur. In the came saturated with respect to potassium chloride, but Searles Lake brine does not contain sufficient sodium carbonate to permit of `we avoid the formation of glaserite through suitable regulation of the temperatures of evaporation and the amount of evaporation taking place at any one temperature. If evaporation indicated in this diagram is not continued to. the int at which the brine becomes saturate with respect to glaserite but is stopped at some point such as B, no such precipitation of glaserite will ractice of our invention we ordinarily emp oy a triple effect evaporator, pass the mixture into the .third or low temperature effect, in which the composition of the mixture is represented by point A, and continue the evaporation in this effect only until such a point as B is reached. The brine, from which preci itated salts have been removed, is assed into the second evaporator pan, in wliich the conditions are approximately as shown by Fig. 3 for 80 C. The concentration 'taking place in the second effect is re resented by the crystallization path B-C lying in the Burkeite face at this temperature. Whereas continued evaporation at the lower temperature would have caused formation and precipitation of glaserite, it may be readily seen by comparison of the two diagrams that the area of the glaserite face is greatly decreased at the higher temperature and that the area of the Burkeite face greatly increased, so that at thishigher temperature a much higher concentrationof potassium chloride may be obtained before any formation of glaserite can occur. Fig. 4 showing equilibrium conditions at 110 C. indicates conditions existing in the first or high temperature effect of a triple effect I evaporator. Reference to this figure shows that continued concentration of .the brine represented by point C in the preceding figure will, at this higher temperature,

cause concentration and crystallization along.

the line C-D with precipitation of only Burkeite. sodium carbonate monohydrate and sodium chloride until the brine becomes saturated with respect to potassium chloride. As may readily be seen the solubility of potassium chloride at this higher temperature is much greater than for either of the lower temperatures and the amount of potassium chloride which can be recovered by chilling of the brine to agiven lower temperature is correspondingly increased. By such suitable evaporation at progressively increasing temperatures we have avoided all formation of glaserite and loss of potash, have obtained a biine highly concentrated with respect to potassium chloride. and have gained these desirable results while employing' multiple effect evaporation and obtaining the great economy and eiciency which is thereby made possible. o

vB reference to Fig. 1, showing equilibrium con itions at 20 C., it will be noted that the crystallization end point Eq. 9 is in equilibrium with potassium chloride, sodium carbonate, heptahydrate, sodium chloride and glaserite. Since this 'point is in equilibrium with glaserite rather than with Burkeite, it is impossible under any conditions to concentrate the brine at this temperature until it becomes saturated with respect to potassium chloride, without also causing saturation with respect to glaserite. The highest concentration with respect to potassium chloride which can be obtained at this temperature without loss of potash, as glaserite, during concentration of brines similar to Searles Lake' brine is tlierefore represented by the int Eq. 8. This oint can onl be reache however, without oss of potas as glaserite, when the brine contains high concentrations of sodium cxirbonate. A similar condition exists at :ill temperatures up to about 50 C. and in order to obtain saturation of Searles Lake brine with potassium chloride without se aration of potash as glaserite final evaporation must in any case be effected at this or a higher teinperature. 'Ihe amount of carbonate naturally present in Searles Lake brine is insufficient to permit of saturation with potassium chloride without loss ofpotasli, as glaserite at this temperature, however, and such saturation can be attained only through addition of substantial amounts of sodium carbonato to the brine or by completing the evaporation at substantially higher temperatures in4 the manner which has been indicated above. Preventing the formation of laserite by completing the evaporation at iiglier temperatures as carried out in the ractice of our invention, is much easier an more economical than adding sodium carbonate.

In the actual eva oratioii of Searles Lake brine in multiple e ect eva orators, according to this invention, the brine, teni orarily, may not be completely saturated wit 1 sodiuni chloride. At ordinary temperature, Searles Lake brine is saturated with sodium chloride and also saturated or nearly saturated with Burkeite. On warming to the temperature of the first effect into which the vbrine is introduced, 57 C. for example, the solubility of the sodium chloride increases and that of Burkeite decreases. Warming alone without any removal of water will, therefore, precipitate Burkeite and render the brine unsaturated with respect to sodium chloride. Initially, for a brief interval, the brine in the low tem )erature effect will accordingly be saturate with Burkeite but not with sodium chloride'. Similar solubilityr changes may take place in the brief interval during which brine is transferred between succeeding eflll tions-governing' concentration at different temperatures may be obtained by calculation from the data of' the polytherms. Our equilibrium diagrams and data may be equally Well used to determine the changes which will tale place in the composition of concentrated brines during cooling andto determine suitable conditions under which a high yield ot pure potassium chloride may be economically obtained -by cooling. Similarly, the data can be'nsed to determine thenecessary coinposition ol the concentrated brine in order that during suitable cooling only the desired changes will talre place Aand that only potassium chloride will be preci itated. llt

obvious that concentration o the brine cannot be carried beyond the point at which it becomes saturated with respect to potassium chloride. As has been previously stated,

Llll

however, the' concentration must be carried at leastto a certain minlmum value,for it l,this is not done there will be a prec1p1tation.

ot sodium chloride and under certain conditions, glaserite together with potassium chloride when the brine is cooled. 'F or any Igiven. temperature ot evaporation, the minimum permissible concentration with respect to potassium chloride above which no sodium chloride will precipitate #on l cooling to say 35, and below which concentration such precipitation of sodium chloride will take place,

may .readily be'determined by means of our equilibrium data.

The conditions which exist during nal concentration of a brine at 110 and cooling to 35, for example, may be followed by reference to Fig. 5, which shows equilibrium diagrams for these two temperatures superimposed upon each other. Point-Clemescnts the initial composition of atypical brine entering the high temperature evaporator.

pan. With further evaporation thepoint titl representing the composition of the brine will move along the line CD, with precipitation ot sodium chloride and Burkeite, and from D along the line D-Eq. 2 with precipitation ot sodium chloride, Burkeite, and sodium carbonate monohydrate until the crystallization `end point, Eq. 2, is reached, or until evaporation is stopped at'some point such as A. Alter evaporation is'stopped andthe solid salts which have been'precipitated are removed, if the brine is cooled to 35 C. its comevaporation from D toward Eq. 2. At D position will change, chiefly through deposit-ion of potassium chloride, until it reaches .equilibrium at some point, such as B, in the changes which take place in the composition of the brine during Vsuch evaporation and cooling may be readily calculated from the data of our polytherms and 4will be briefly illustrated in the following example.

During evaporation at 110 C. from D to- 'ward Eq. 2 the concentration of the brine with respect to potassium chloride will increase, with respect to sodium carbonate and sodium sulphate will change but slightly, and the solubility and concentration ot sodium chloride will stealdly decrease. 'If evaporation is stopped at any point A between D and Eq. 2 and after separation of the recipitated salts the brine is cooled to 35 the solubility ot the potassium chloride will decrease,

cooling, the solubility ot the sodium chloride,

which is shown in the complete data of the polytherms but not on the diagrams, vmay or may not decrease, to cause crystallization and contamination of the potassium chloride, depending on the extent to whichthe evaporation has been carried. For any position ot the point A at which evaporation is stopped, between the limits D andA Eq. 2, the correspondingvalues of B, after cooling to 35, will not be greatly changed. A solution evaporated to any value A between these limits will therefore, on coolin to 35 C., reach a final composition B whic i is not ve far from constant. It has been said that the solu- .causing crystallization and precipitation of bility of sodium chloride decreases during the brine will hold more sodiumchloride, and at Eq. 2 will hold less, than can be held in solution at the more or less constantrcorresponding positions of B. In the first case, cooling will cause a decrease in sodium chloride solubility and objectionable precipitation; in the second case, cooling from Eq.=2.

there will be an increase in solubility. At some position of A between the .limits D and Eq. 2, therefore, the solubility of'sodium chloride at the higher temperature, 1l()O C., will be the same as after cooling to 350. and in this case precipitation ot sodium chloride to contaminate the potassium chloride obtained on cooling will just be prevented. This value of A can readily be calculated from the data of the polytherms, and represents the minimum concentration, to a value between which and the concentration represented by Eq. 2, thebrine should be evapo rated in order to obtain on coolin a potassium chloride salt freeA from so lum chloride.

`Therefore, if yevaporation of the brine is carried out under the suitable conditions vwhich have been indicated until its composition is represented by some point between the minimum value A and the c stallization end point Eq. 2, the concentrate brine ma then be cooled to C. to give a high yleld of potassium chloride free from sodium chloride. If separation of borax from the brine until after the potassium chloride has been removed'is suitably prevented by rapid cooling as described below, the potassium chlo' ,ride which separates from such a concen trated brine on cooling will be of very high purity. lVe have found that if the final evaporation is carried out at a temperature of 110 C., the maximum possiblel concentration representing saturation with respect to potassium chloride at this temperature is nearly 47 mols per 1000 mols `of water and the minimum` concentration to prevent separation of sodium chloride on cooling as indicated above .is-o nly slightly over 41 mols. These maximum and minimum values are indicated forv various temperatures of concentration in It will be noted that as the temperature of evaporationis decreased from 110? C., the maximum andminimum values approach each other.` Atthe higher temperature there is a fairly wide range Within which concentration can be stopped without having caused vsaturation and precipitation of potassium chloride on theone hand, and without causyie ds of potassium chloride oncooling, and

at the.. same time the permissible'range of concentration within which the evaporation can be suitably stop ed is increased to a considerable extent. (Iloncentra-tion at a final temperature kof 110 C: followed by cooling to 359 C., for example, gives more than double the yield over concentration at a final telnperature of C. followed by cooling to '35 C. This is of great advantage in the commercial operation of the process, because of the lncreased yield and because limitations of mechanical and analytical control of the evaporation make it diflicult, not impossible, toalways carry the concentration ex, actly to the point of saturation with, potassium chloride.

In order to promote the crystallization of pure potassium chloride and prevent borax rom separating withit on cooling of the concentrated brine; it is important to cool the brine very rapidly, .in not over two Kto three hours for example, and preferably much less,

from the higher to the lower telnperature.

In practice, ordinarily it is carried from about 110o to about 30. By rapid cooling in this way no appreciable amount of borax crystallizes out because of its slower crystallizing tendency. The borax remains. in super-saturated solution and can afterwards be separated from the mother liquor by slower crystallization. We have found that the presence of sodium borates in moderate quantities does not appreciably affect the behavior of the other salts durin concentration, and does not interfere with t e separation of pure potassium chloride during suitable rapid cooling. On standing, however, for a further period of time the borax will crystallize out and can be recovered as 'one of the valuable products of the process. If the borate content of the concentrated brine is equivalent to not over 7 or 8% of sodium tetraborate, it is possible to produce potassium chloride, containing less than 0.5% borax by the method above described, and this figure may be materially reduced by operating under favorable conditions such as decreased concentration of borates in the concentrated liquor and more rapid cooling.

In the continuous o eration of the process,

the mother liquor, rom which potassium chloride and bora-x have been largelyremoved by crystallization, may be advantageously returned to the process, together with certain wash liquors which will be further indicated, and admixed with the raw brine for further recovery of potassium chloride and borax.l Such return of mother liquor 'and .wash liquors will correspondingly modify the composition of the brine entering the evaporator, but this change in the composition of the brine is not ordinarily great enough to necessitate material change from the control conditions as outlined. Compared with the raw brine alone, the concentration of a mixture of mother li uor and wash liquor will ordinarily be hig 1erl with respect to sodium carbonate and potassium chloride. An increase of concentration with respect to potassium'chloride alone increases the tendency towards formation of glaserite during evaporation. The increase of concentration with respect to sodium carbonate tends to reduce the tendency towards formation of laserite and it will further be foundl that under normal conditions the crystallization paths of the feed liquor obtained by mixing raw brine, mother liquor and wash liqproximately 57 C. and the following work will be effected during the time that the brine is evaporated in this pan:

Removed by evaporation, 366 tons water.

Removed by preCipitatiOn-Burkeite' 101 tons, NaCl 60 tons.

From this evaporator pan approximately 444,000 gallons of brine will be transferred to the pan at next higher temperature. Tn this pan the temperature is maintained at approximately C. and the following work will be effected during the time that the brine is evaporated in this pan:

. Removedb evaporation,water478 tons.

Removed y precipitation- Burkeite G3 tons, NaCl 136 tons.

From this pan there will in turn remain 318,000 gallons of brine which are transferred during the operation of the cycle to the high temperature pan. In this pan the temperature is maintained at approximately 110o C. and the following work will be effected during the time that the brine is evaporated in this pan:

Removed by evaporation, 517 tous of water.

Removed by precipitation-Burkeite 30 tons, NaCl 150 tons, NazCORlHZ() 61 tous.

From this pan there will in turn remain 163,000 gallons of concentrated liquor of suitable composition for recovery of potassium chloride and borax by suitable cooling. This liquor will contain approximately the following:

Tous. Hgo i 50e KCl 18S NaCl 80 Naso4 e Nincox 70 Namo, ce

Tn order .to obtain pure potassium chloride' from cooling of concentrated brine, it is absolutely essential that all other salts which have been precipitated during the course of the evaporation should be completely removed, and that the concentrated brine shall contain no solid salts in suspension. .ln order toeifect such a complete removal of all precipitated salts during evaperation, we use salt traps for collecting such salts from each evaporator pan. These are so arranged that the brine from each pan is circulated through one of these traps where, due to slow circulation, the suspended salts are practically completely precipitated, after which the clear brine is largely returned to the same pan from which it was drawn. A part of the brine from the lower temperature pan7 however, is passed on to the next evaporator pan as required to maintain suitable level in each pan. Two or more of these salt traps are used for each evaporator pan in order that one may remain in operation while the other is being emptied of precipitated salts, whereby continuous evaporator operation is maintained. Before emptying these salt traps, the preciptated salts are washed ,with raw brine for removal of the concentrated brine contained therein, such wash liquors being returned to the mixed liquors for further evaporation and recovery of their contents. Through proper use of such salt traps it is possible to obtain a concentrated liquor such as has been described above, which contains no suspended salts and from which pure potassium chloride, and substantially pure borax, may be obtained by suitable cooling.

Rapid cooling is carried out in order to bring the temperature down to approximately 300 C. within less than three hours. By means ot' such rapid cooling, in the absence of solid borax salts, crystallization of potassium chloride only will take place,.tl1e brine remaining ina condition of supersaturatiou with respect to borax. TWhen the brine has reached the lower ten'ipcrature and crystallization of the potassium chloride is practically complete, the cooled mixture ol' potassium chloride crystals and liquor is pumped into a settling tank and allowed to stand for about 20 minutes. At the end of this period,

the clear liquor is sent to cooling tanks :tor

further cooling and the sludge remaining in the bottom of the settling tank is sent to'thc centrifuges.

In the centrifuges, potassium chloride crystals are separated from most of the accompanying liquor andthen washed with water to free them from the remaining liquor. The liquor and wash water mixture from the centrifuges is added to the liquor decanted from the settling tanks and sent to the cooling tanks. The potassium chloride salts are removed from the. centrifuges and sent to the storage piles. These salts contain all the potassium chloride recovered in the process. i

The combined liquor from the potash settling tanks and centrifuges is brought down to a temperature of about. 9,00 C. in the cooling tanks and then transferred to storage vats where the sodium tetraborate, with. respect to which the solution h as been supersatiuatod, slowly7 crystallizes out. After this crystallization, which may take twelve hours or more, is completed, the mother liquor is allowed to drain ofi' into a sump where. it is mixed with raw brine for return to the process cycle. The remaining sludge, which cou`- sists principally of borax but contains considerabley quantities of potassium chloride and mother liquor, is sent toa hot dissolver.

where it is heated to boiling with a sufiicient quantity of water added to bring the sodium tetraborate concentration down -to about 20%. The liquor is passed hot through a pressure filter Aand then cooled to about 40 C. in a crystallizer with agitation. The borax which separates is passed, together fil With the borax mother liquor, to settling tanks. After a period of settling the clear liquor is decanted and the bora): sludge dropped to centrifuges for removal of the remaining liquor, with a final Wash in the centrifuges. No further purication of the borax is necessary. lDecanted and Wash liquors are returned to the process.

life claim:

1. An improvement in concentrating brines containing carbonates, sulphates and chlorides of sodium-and potassium, which are substantially saturated with sodium chloride and contain lessthan the amount of sodium carbonate necessary to saturate the brine, which consists in evaporating the brine to a concentration less than that at which formation of glaserite begins, increasing the temperature and continuing the evaperation.

2. An improvement in concentrating brines containing carbonates, sulphates and chlorides of sodium and potassium, which are substantially saturated With sodium chloride and contain less than the. amount of sodium carbonate necessary to saturate the brine, which consists in evaporating the brine above about L19 C. to a concentration less than that at which formation of glaserite begins and more than that below Which sodium chloride Will separate on cooling.

3. An improvement in concentrating brines containing carbonates, sulphates and chlorides of sodium and potassium, which are substantially saturated With sodium chloride and contain less than the amountv of sodium carbonate necessary to saturate the brine, which vconsists in evaporating the brine above about 49 C. to a concentration less than that at which formation of glascrite begins and continuing the evaporation at a higher temperature to a'concentration more than that below which sodium chloride will separate on cooling.

4. An improvement in concentrating Searles Lake brine, which consists in evapof rating the brine in tripple effect evaporators, first at atemperatureof about 57 C.,then about and finally about 110 C., transferring the brine to each successively higher temperature effect before formation of glaserite begins at Athe prevailing temperature and concentration, and evaporating the brine in the final effect to a concentration of more than about 41 mols of llgCl2 per 1000 mols of Water.y

more than about l1 mols of Kztll, per 1000 mols of Water and less than about amols of KgCl2 per 1000 mols of Water.

0. An improvement in concentrating Searles Lake brine, which consists in concentrating the brine by evaporation at a final temperature of about 110 C. to a concentration of more than about l1 mols of Kglz per b1000 mols of Water.

1. An improvement in concentrating Searles Lake brine, which consists in concentrating the brine by evaporation at a final temperature of about 110 C. to a concentration of more than about 41 mols of M2012 per 1000 mols of Water and less than about 4'? mols of MgCl2 per 1000 mols of Water.

8. An improvement in recovering potassium chloride from brines containing carbonates, sulphates and chlorides of sodium and potassium, which are substantially saturated With sodium chloride and contain less than the amount of sodium carbonate necessary to saturate the brine, Which consists inv evaporating the brine above about 49 C., to a concentration less than that at lwhich separation of potassium salts begins and cooling the concentrated brine to a temperature at which sodium chloride is at least as soluble as at the final evaporation temperature.

9. An improvement in recovering potassium chloride from Searles Lake brine, which consists in evaporating the brine in triple effect evaporators, first at a temperature of about 57 C., then about 80, and finally about 110 C., transferring the brine to successive higher temperature edects before formation of glaserite begins at the prevailing temperature and concentration and cooling the concentrated brine to about 30 U.

10. An improvement in recovering potassium chloride from Searles Lake brine, which Consists in evaporating the brine in triple effect evaporators, first at a temperature ofabout 57 C., then about 80, and nally about 110 C., transferring the brine to successive higher ltemperature effects before formation of glaserite begins at the prevailin temperature and concentration, cooling the concentrated brine to about 30 C., separating potassium chloride, further cooling the brine to about 20 C. and separating boraX.

11, An improvement in recovering potassium chloride from Searles Lake brine, Which consists in concentrating the brine by evaporation at a final temperature of about 110, (Lto a concentration ofmore than about 41 mols of K2Cl2 per 1000 mols of Water, cooling the concentrated brine to a temperature at which sodium chloride is at least as soluble as at the final evaporation temperature, separating potassium chloride, further cooling the brine and separating boraX.

12. An improvement in recovering potassium chloride from brines containing carbonates, sulphates, chlorides and borates of sodium and potassium, which 'are substantially saturated with sodium chloride and contain less than the amount of sodium carbonate necessary to saturate the brine, which consists in evaporating the brine above about 49 C. to a concentration less than that at which formation of glaserite begins, continuing evaporation at a higher temperature, cooling the concentrated brine to a temperature at which sodium chloride is at least as soluble as at the iinal, evaporation temperature, se aratng potassium chloride, further cooling t e brine and separating borax.

13. An improvement in concentrating Searles Lake brine, which consists in evapotures.

HARALD DE BOPP. WILLIAM E. BURKE. 

